The left and right headlamps of a motor vehicle conventionally generate identical beams that are essentially superimposed at a distance from the vehicle.
Accordingly, on a standardized projection screen at a distance of 25 meters the two beams have respective concentration spots with a cumulative effect and the lateral edges of the beams are essentially superimposed.
This applies to the low beam and to the high beam and the superimposition is achieved by virtue of the fact that the optical axes of the reflectors of the two headlamps are both essentially parallel to a longitudinal vertical plane of the vehicle.
FIG. 1 of the accompanying drawings shows the front part of a modern motor vehicle. It should be noted in particular that the bodyshell C and the front-glasses Gg and Gd of the left and right headlamps Pg and Pd are curved and streamlined towards the sides of the vehicle.
As shown, this leads to the use of respective reflectors Mg and Md which are relatively deep on the interior side and relatively shallow on the exterior side. This constraint raises two essential problems. The first is the difficulty of generating at each headlamp a wide horizontal spread towards the opposite side of the road because the depth of the part of the reflector on the interior side can block the propagation of steeply inclined light rays. Another problem is the reduced luminous flux recovered by the reflector because the exterior part of the reflector has a very small depth.
Referring now to FIG. 2, it will be apparent why the geometry of headlamps like those shown in FIG. 1 could make them particularly likely to generate light beams with a wider spread towards the outside than towards the inside, as shown by the paths of the rays represented in FIG. 2.
Accordingly, by tilting the beam from the left headlamp towards the left and the beam from the right headlamp towards the right a wider overall beam would be obtained without encountering the usual design problems that arise on attempting to increase the width of a beam (downward folding of images of the filament if striations are deposited on an inclined front-glass, lack of homogeneity if a plurality of reflector areas generate beam paths with different widths which must be mixed to form the overall beam).
However, and referring now to FIG. 3, a problem that would arise with any such lateral offsetting of the beam would be that the two beams Fg and Fd would mix highly imperfectly and in particular the lateral edge of each beam on the interior side, being near the axis of the road, would cause a marked step (S) in the level of illumination of the overall beam, which is totally undesirable.
An object of the present invention is to mitigate these limitations of the prior art and to provide a pair of motor vehicle left and right headlamps that combine to form a wide beam without causing problems of lack of homogeneity in the combination.
Accordingly to the present invention, there is provided a set of left and right motor vehicle headlamps, each headlamp including a reflector associated with a light source and a closure front-glass, characterized in that the left and right headlamps are respectively adapted to generate horizontally spread left and right illumination beams, each beam having a fuzzy edge on the left and on the right, said edges being asymmetric relative to the axis of the road; in that the left edge of the left beam is offset angularly to the left relative to the left edge of the right beam; and in that the right edge of the right beam is offset angularly to the right relative to the right edge of the left beam.
The following are preferred but non-limiting aspects of a set of headlamps in accordance with the invention:
the reflector of each headlamp has a plurality of smooth reflecting surface areas juxtaposed laterally to each other and delimited by transition lines of broken slope, at least one of said areas being adapted to spread light horizontally between extrema obtained in the immediate vicinity of said transition lines, and the horizontal spreading extremum of each area varies progressively along the transition line concerned; PA1 the horizontal generatrices are adapted to assure spreading by divergence; PA1 the horizontal generatrices of the various areas and the position of their transition lines are such that, from the center towards the lateral edges of the reflector, the horizontal spreading extrema in each area diminish progressively; PA1 the horizontal spreading with asymmetric edges is assured by a back area of the reflector of each headlamp; PA1 at least one edge area of each reflector is adapted to generate a beam part essentially concentrated on the axis of the road and the concentrated beam parts generated by the two headlamps are essentially superimposed in front of the vehicle; PA1 the light source of each headlamp is defined by a lamp mounted axially in a lamp hole in the reflector and the axes of said lamps and said lamp holes of the left and right headlamps are respectively obliquely inclined outwards relative to the longitudinal axis of the vehicle; PA1 the back area of each reflector is generally symmetrical about the oblique axis of the lamp and the associated lamp hole; PA1 at least one edge area of each reflector has an essentially parabolic horizontal generatrix with its axis substantially parallel to the longitudinal axis of the vehicle; and PA1 each reflector is injection molded from a plastics material with a mold removal axis corresponding to the axis of the lamp and of the lamp hole.
The invention finds an application mainly, although not exclusively, in low beam headlamps and fog lamps and where appropriate in widebeam high beam headlamps.